Landfills, in particular those used for the disposal of municipal waste, generate significant amounts of gas as the waste matter within the landfill breaks down. Greenhouse gases, such as methane and carbon dioxide, comprise a large constituent of the gas, and result from the breakdown of cellulosic material, for example, paper, wood, yard waste as well as other organic matter. Landfills also produce large quantities of leachate. Leachate is caused primarily by precipitation (rainwater) percolating through the waste deposited in the landfill. Other sources of leachate derive from the biological breakdown of waste matter in the landfill as well as the recirculation of leachate and other liquids through the landfill. In the course of passing through the waste matter, the various liquids extract soluble or suspended solids, as well as other components of the decomposing matter. To prevent the leachate from contaminating the groundwater, expensive and sophisticated impermeable liners are installed between the waste matter and the soil underlying the landfill.
Challenges faced by landfill designers and operators include efficient and thorough removal and treatment of gaseous by-products to mitigate or prevent gas discharge to the atmosphere and environmentally responsible collection and treatment of the leachate to prevent groundwater pollution, while maintaining stability of the landfill and protecting the integrity of the liner. These challenges become more acute as the depth of landfills increase in response to ever greater expenses associated with constructing and operating landfills. There is clearly a need for structures which provide for the efficient draining of leachate and for the thorough extraction of gases from all levels of the landfill.